1. Field of the Invention
The present invention relates to a microstructure equipped with a dielectric base material having a plurality of fine holes in the surface thereof and metal members capable of inducing local plasmon, a method for producing the microstructure, and an optical field amplifying device that utilizes the microstructure.
2. Description of the Related Art
Light energy transfer elements that efficiently utilize solar energy, are being considered. Solar energy is being investigated as a new, clean, and safe alternative energy source to replace fossil fuels such as oil. The photosynthesis function of plants has been noted as a highly efficient method of light energy transfer, and there is expectation for development of artificial light energy transfer elements (artificial photosynthesis elements) equipped with artificially constructed photosystem complexes that have photosynthesis functions.
Japanese Unexamined Patent Publication Nos. 2001-303022 and 2002-25635 disclose light energy transfer elements (photoelectric conversion systems). These light energy transfer elements are equipped with: a metal or semiconductor base material; and a mixed self assembled monolayer. These light energy transfer elements are easy to produce, and light which is absorbed by the complex can be highly efficiently converted to energy. However, because the film thickness of the monolayer is several nm, the absorption efficiency of incident light is extremely low.
In order to obtain higher efficiency, light energy transfer elements that employ microstructures having electric field amplifying effects on the surfaces thereof as the base material on which the photosystem complexes are provided are being considered. Japanese Unexamined Patent Publication No. 2005-259674 discloses a photoelectric conversion element. In this photoelectric conversion element, photosystem complexes are formed on a microstructure constituted by electrodes which are formed by accumulated gold nanoparticles. The high specific surface area of the gold nanoparticles and an electric field amplifying effect caused by local plasmon enables highly efficient photoelectric conversion of incident light, by photosystem complexes which are immobilized on the electrodes at high density.
PCT Japanese Patent Publication No. 2004-530867 discloses an optical amplifying substance, in which a plurality of agglomerated nanoparticles (including fractals) are provided in the vicinity of microcavities, as a microstructure having an electric field amplifying effect. U.S. Pat. No. 7,288,419 discloses a microstructure equipped with a dielectric base material and a plurality of fine metal particles. In this microstructure, highly densely arranged fine holes are provided in the surface of the dielectric base material, and each of the metal particles includes a filling portion that fills a fine hole, and a head portion that protrudes from the surface of the dielectric base material and which are of a size capable of inducing local plasmon resonance.
However, in the microstructures disclosed by Japanese Unexamined Patent Publication No. 2005-259674 and PCT Japanese Patent Publication No. 2004-530867, the bonds between the metal particles that constitute the photosystem complexes and the base materials are weak. Therefore, the metal particles flake off easily, and it is difficult to stably hold the photosystem complexes. Accordingly, it is difficult to realize uniform function across the entire surfaces of the microstructures.
In the microstructure disclosed by U.S. Pat. No. 7,288,419, the metal particles which are capable of inducing local plasmon are embedded in the base material. Therefore, the metal particles are less likely to flake off than in the structures disclosed by Japanese Unexamined Patent Publication No. 2005-259674 and PCT Japanese Patent Publication No. 2004-530867.
However, it is necessary to form the metal particles such that a single head portion corresponds to each filling portion that fills the fine holes, which are arranged at high density within the surface of the dielectric base material. The process for forming a head portion for each of the plurality of filling portions, which are microstructures on the order of nanometers, is not easy, and there is a possibility that yield will suffer.